Hi, I am new to keil and I am learning how to use the interface. An "x" appears in the device icon, it has no problems when compiling but my program does not work, I do not know if it is because of this.
Look up "File, Group and Attribute Icons" in the Keil help. This icon means "File with incompatible modifications. A file update is required." Try opening the context menu on those files (mouse right click) -- there should be an update option on the context menu. If the file is updated, edits you made to the original file, such as heap size, won't be preserved and you'll have to apply those changes again.
Here is the manual page to clarify it
www.keil.com/.../uv4_ca_updswcmpfiles.htm